Thermostat Kit, 160° – Fits MerCruiser V6 & V8 Engines (Replaces 807252Q5)

$18.49

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Thermostat Kit, 160° – Fits MerCruiser V6 & V8 Engines (Replaces 807252Q5) is backordered and will ship as soon as it is back in stock.

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Delivery and Shipping

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This Thermostat Kit, 160° – Fits MerCruiser V6 & V8 Engines (Replaces 807252Q5) is designed for MerCruiser V6 and V8 engines including 4.3L, 5.0L, 5.7L, 7.4L, and 8.2L models from 1987–2016 equipped with standard cooling systems. It ensures your engine operates at the correct temperature for optimal performance and efficiency.

This kit serves as a direct replacement for Quicksilver/Mercury part numbers 807252Q5, 807252T5, and 807252T8, as well as Sierra part 18-3647.

Engineered for direct OEM replacement and fitment.
Maintains a consistent 160°F (71°C) operating temperature.
Complete kit includes thermostat, plastic sleeve, and all necessary gaskets for installation.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Quicksilver / Mercury	807252Q5
Quicksilver / Mercury	807252T5
Quicksilver / Mercury	807252T8
Sierra	18-3647

Engine & Model Compatibility

Confirm your engine model/year in the table below.

This thermostat kit is specifically designed for a wide range of MerCruiser engines. Please verify your engine model and serial number range to ensure correct fitment.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
MerCruiser	4.3L V6	4.3L V6	4-Stroke	1987–2016	807252Q5	Standard cooling only
MerCruiser	200 / 5.0L	5.0L V8	4-Stroke	1987–1995	807252Q5	Serial: 0B525982–0F600999
MerCruiser	230 / 5.0LX GM	5.0L V8	4-Stroke	1987–1995	807252Q5	Serial: 0B525982–0F600999
MerCruiser	260 / 5.7L GM	5.7L V8	4-Stroke	1987–1995	807252Q5	Serial: 0B525982–0F600999
MerCruiser	262 MAG Alpha	5.7L V8	4-Stroke	1996–1997	807252Q5	Serial: 0F803800–0K999999
MerCruiser	262 MAG Bravo	5.7L V8	4-Stroke	1996–1997	807252Q5	Serial: 0F803800–0K999999
MerCruiser	350 MAG	5.7L V8	4-Stroke	1987–1997	807252Q5	Serial: 0B525982–0F600999
MerCruiser	350 MAG EFI Ski	5.7L V8	4-Stroke	1994–1997	807252Q5	Serial: 0D505450–0K999999
MerCruiser	350 MAG MPI / M IE	5.7L V8	4-Stroke	1998 & Up	807252Q5	Serial: 0L010019 & Up
MerCruiser	350 MAG MPI Ski	5.7L V8	4-Stroke	1995–1998	807252Q5	Serial: 0F350583 & Up
MerCruiser	350 MAG Ski	5.7L V8	4-Stroke	1991–1997	807252Q5	Serial: 0D505450–0K999999
MerCruiser	7.4L / 8.2L V8	7.4L/8.2L V8	4-Stroke	1987–2016	807252Q5	Standard cooling only

Technical Specs

Product Type: Thermostat Kit with Gaskets
Installation: Direct OEM Replacement
Temperature Rating: 160°F (71°C)
Connection: Standard MerCruiser Cooling System
Housing Material: Brass with Plastic Sleeve
Housing Sleeve: Plastic (23-806922)
Weight: 0.2 lbs (0.09 kg)
Warranty: 1 year factory warranty against defects
Other Technical Attributes: For use in standard cooling systems only, not high-performance engines

What’s in the Box

1 x Thermostat (807252T2)
1 x O-Ring Seal
1 x Cork Gasket (27-48818-1)
1 x Solid Housing Gasket (27-33179-2)
1 x Open Housing Gasket (27-47510)
1 x Open Base Gasket (27-53045-1)
1 x Open Base Gasket with Ground Rivets
1 x Plastic Sleeve (23-806922)

Installation Notes

Ensure the engine is completely cool before starting. Disconnect the battery for safety.
Drain the engine coolant into a suitable container. Locate the thermostat housing on the engine.
Remove the bolts securing the thermostat housing. You may need to gently tap the housing to break the seal.
Remove the old thermostat and all gasket material. Note the orientation of the existing thermostat.
Thoroughly clean both the housing and engine block mating surfaces to ensure a perfect seal.
Install the new thermostat in the same orientation as the original. Place the correct new gasket(s) into position.
Reinstall the thermostat housing and tighten the bolts to the manufacturer's specified torque.
Refill the cooling system with the appropriate coolant.
Reconnect the battery, start the engine, and let it warm up. Carefully check for any leaks around the housing.

Troubleshooting & FAQ

What are the signs of a failing thermostat?

Common symptoms include engine overheating, engine temperature fluctuating erratically, or the engine taking too long to reach its normal operating temperature. You may also notice coolant leaks around the thermostat housing.

How can I tell if my engine has a "standard" cooling system?

Standard cooling systems are typically found on stock, recreational MerCruiser engines. High-performance, racing, or modified engines often have closed or high-capacity cooling systems. If you are unsure, consult your engine's service manual or a qualified marine mechanic.

My engine is still overheating after replacing the thermostat. What else could be wrong?

If overheating persists, other potential issues include a faulty water pump impeller, clogged heat exchanger or risers, a collapsed coolant hose, or an airlock in the cooling system. Always diagnose the entire cooling system if a new thermostat doesn't solve the problem.

Is there a specific way to install the thermostat?

Yes, thermostats are directional. They must be installed with the spring-loaded, heat-sensing element facing the engine block side to correctly sense coolant temperature. Installing it backward will prevent it from functioning properly.

OEM vs. Aftermarket?

This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.

Shipping speed & cost?

We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.

Warranty & returns?

Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.

Safety & Important Info

Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
This is an aftermarket replacement, not an OEM component.
Professional installation is recommended for safety and performance.

About Sea Sierra

Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

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